Double propeller for water and air craft



April 28, 1925.

R. WAGNER DOUBLE PROPELLER FOP WATER AND AIR CRAFT Filed De. so. 1919 Patented Apr. 28, 1925 RUDOLF WLGNEIQ, OF HAMBURG,

GERMANY, LTD. A./S., or CHRISTIANIA, NORWAY.

ASSIGNOR T0 STAR GON'IRAPROPELLER DOUBLE PROJPEIL ER FOR WATER AND AIR CRAFT.

Application filed December 30, 1919. Serial No. 348,388.

To all whom it may cmwern:

Be it known that I,'Doctor Ruoonr WAG- NEH, chief engineer, a citizen of the German Republic, residing at Hamburg, Germany, Bismarckstr. 105, have invented certain new and useful-Improvements in Double Propellens for Water and Air Craft, of which the following is a specification.

This invention comprises improvements in and connected with screw propellers particularly applicable for the propulsion of water craft and aerial craft.

Tn known types of marine propellers in combination with fixed counter propellers arranged behind the principal propeller in the normal direction of travel, the diameter of the counter propeller is approximately as large as the diameter-of the main propeller. The intention being to utilize, as far as possible and by means of the tired guide blades. the tangential motion of the water close to the periphery of the propeller. In

order to further achieve this purpose, it has also been suggested to make the counter propcllcr of even larger diameter than the main propeller.

Tn practice, these types oil double lers have been drawbacks. the counter propelfound to possess considerable For example, the outer parts 0% propeller are easily damaged when the ship happens to ground or to strike did against a bank or object. Experience has shown, also, that by the strong rhythmical "ariation of the direction of flow to which the outermost threads of water are subjected, according: to the varying distance between the blades of the main propeller and the blades (if the counter propeller, seen-in the direction of rotation, the .outer parts of the counter propeller blades are subjected to considerable bending stresses. These stresses increase as the diameter of the counter propeller approaches, or even exceeds, that of the main propeller. Therefore, the blades of the counter propeller have, in such cases, to be made stronger at their inner sections, thereby involving the disadvantage ot an increased axial resistance to the flow. The gain at the outer periphery is therefore again partly compensated by the 'loss at the inner parts; besides thestrengthening of such inner partsobviously entails a greater weight.

Tn conslderation of these circumstances and according to the present invention, a diameter is deliberately adopted for the counter propeller, arranged behind the principal propeller, which is smaller than the diameter of the main propeller: in order to render such construction feasible without impairing the maximum efliciency ofl the propeller, the present invention further pro vides that the main propeller has a variable pitch increasing radially towards the hub. Thereby the tangential action of the water is reduced at the periphery but 'is more powerful in the centre. Therefore, the outermost parts or the counter propeller, under such conditions, may be dispensed with, as the comparatively small gain due to their retention would be discounted by the displacement and frictional such parts.

The radial variation of pitch is, in this case, not only to be understood in the ordinary way, that is to say having relation to the, variation of the pressure surface of the screw, but it embraces the variation of the so-called efi ective pitch. According to modern views, for instance, a propeller with a constant pitch of the pressure surface may be considered as having a certain radial resistance due to pitch increasing-from. outside to inside owf ing to the thickness of the blades increasing towards the hub or boss.

The increased tangential motion of the water in the centralsections will naturally entail an increasednecessity of providing a counter propeller, and in addition, the elliciency of such counter propeller under these conditions is especially favourable.

Numerous experiments with ordinary single propellers have shown that a radial variability of pitch does not adord any increase of the efliciency worth mentioning. Only when sucha propeller is in co-operation a counter propeller, does the employment of a pitch radially increasing towards the centre become reasonable and its advantage become apparent.

Tn this case,

propeller main prowith the action of the main prov peller is concentrated to the centre and thereare thus complementary and afiord the advantage of a smaller, safer, lighter and cheaper counter propeller.

In general, it may he said, within certain limits, that the counter propeller may he made reduced in diameter accordingly as the pitch of the main propeller is varied or is increased towar s the centre. @bviously there are certain limits for such increase of pitch. Most recent experiments have shown that the diameter of the counter-propeller should not be larger than approximately 0.90 to, the maximum, 0.95 times the diameter of the main propeller. For instance in case of too great an increase of pitch the outer surface of the main propeller may no longer produce a thrust, and, on the other hand, strong eddies may he formed behind its inner hlade sections.

lhe relation between the diameter of the counter propeller and the variations of the pitch of the main propeller may he an inverse linear relation and it may also be determined by any rule of inverse ratio.

The invention is not concerned with a known arrangement of double propeller with fixed d recting; blades or distributors mounted in front of the principal propeller in the direction of travel and having a smaller diameter than the principal pro peller. This arrangement involved a fundamentally diiierent principle inasmuch as t 1e directing or distributing blades of counter propeller communicated to ti o water a tangential sneed opposite direction to that of revolution. of the principal pro peller prior to such water coming into coin tact with the principal propeller.

In order to enable the present invention tobe readily understood, reference is to the accompanying drawing which Fig. 1 illustrates in side elevation one construe tional example of a propulsion device comprising a main propeller and acounter propoller in accordance with these improvements mounted at the stern oi a boat;

Figs. 2, 3, 4; and 5 are transverse sections taken on lines l-1, 2-2, 3--3, and 4-41 of Fig. 1 respectively;

Fig. 6 is a rear elevation of the device shown in Fi 1.

in the drawing, a is the main propeller with its pitch increasing radially towards the boss, or huh at the center, the emerging or trailing edge I) being straight in side elevation for simplifying the construction of the fixed counter propeller o. lhe diameter D of the latteris, according to the present invention, smaller than the diameter D of the main propeller a, for sake of greater safety of service, this diameter has been made even smaller than indicated by the aforesaid limit of O.9-0.95.

In the embodiment shown, the counter propeller 0 consists of ii blade-like arms, which may be either made in one piece with a common hulo a? or separately attached to such a hub.

The vertical blades registering with the rudder stem may also be made in form of a main arm, hollow, it necessary, which may serve for attaching the counterropeller to the hull of the ship, and which ror this purpose may be connected with the rudder stem a, for instance, by means of bolts f, g, 7?, or any other -means. After the screws f, g, 71, and the divided fixed protection hood have been removed, the counter-propeller a may be drawn away sideways from the stem, and the main propeller a may he taken on.

'V'Vith twin-screw ships the counter-proseller may be attached by two oi its blades eing elongated up to the hull of? the ship.

I claim and desire to secure by Letters Patent of toe United States, is:

'opeller for water and airg a rotary main propeller which have pitch in towarl their axis of:

craft, compri fitted CIEdS' 1 proller, the more the radial lain propeller is upon one propeller, the peller he pitch of 2. double propeller comnr toting main propeller with hlados which have a -pitch increasing radially towards the centre, and a fixed counter propeller arranged behind the main propeller and composed of fixed curvilinear hiades, and having a diameter smaller than the diameter of the main propeller and inversely dependent upon the variation of the pitch of the ma1n propeller, the said character being reduced in accordance with the increase 1n the radial pitch of the main propeller.

Du. RUDOLF WAGNIIR. lVitnesses Hemmer; ()EHLERT, Hans Pm 

